Trimming is a post-manufacturing technique for adjusting one or more operating parameters of a circuit provided on a semiconductor die. When forming a circuit on a semiconductor die, there are numerous variables that may affect the operation thereof. Accordingly, sensitive circuits such as radio frequency (RF) circuits are often manufactured including a number of passive components whose resistance, capacitance, and/or inductance may be adjusted and/or a number of active components (e.g., field effect transistors, bipolar junction transistors, diodes, etc.) whose size may be adjusted via a trimming process. The adjustable passive components are provided with a number of “fuses,” usually in the form of small metal traces, which may be cut or destroyed using a laser. By cutting these fuses, the resistance, capacitance, and/or inductance of the adjustable component is changed to a desired value. Similarly, by removing various portions of the active components, a size thereof may be adjusted. Accordingly, one or more operating parameters of the circuit may be adjusted, such that changes in the operation of the circuit due to external factors such as parasitics, manufacturing intolerances, mechanical stress, carrier-die interactions, and the like may be compensated for.
FIG. 1 shows a conventional adjustable resistor 10 whose resistance value may be changed via trimming. The conventional adjustable resistor 10 includes a number of resistive elements R1-R5 and a number of fuses F1-F3. While the resistance of the conventional adjustable resistor 10 is initially set at R1+R2, any of the fuses F1-F3 may be cut in order to add to the resistance of the conventional adjustable resistor 10 as desired. For example, a first fuse F1 may be cut such that the resistance of the conventional adjustable resistor 10 is set at R1+R2+R3. The remaining fuses F2 and F3 may similarly be cut in order to add to the resistance of the conventional adjustable resistor 10.
In order to trim components on a semiconductor die, the components generally must be accessible by a laser. That is, the components must be visible through a transparent or semi-transparent material or openly exposed to the outside environment such that the laser can reach the portions thereof available for trimming. Accordingly, trimming generally occurs through a frontside of a semiconductor die on which the components are either surrounded by a transparent or semi-transparent material, such as an oxide or thin-film semiconductor layer, or openly exposed. A backside of the semiconductor die is generally covered by a thick opaque semiconductor die material and thus trimming cannot occur through it. FIGS. 2 and 3A-3C illustrate a conventional trimming process.
First, a semiconductor die 12 including a number of components 14 coupled together to form a circuit is provided (step 100 and FIG. 3A). The semiconductor die 12 shown in FIG. 3A is a semiconductor-on-insulator (SOI) semiconductor die including a substrate 16, an insulating layer 18 over the substrate 16, and a device layer 20 over the insulating layer 18. The components 14 are formed in the device layer 20, and are separated from the substrate 16 by the insulating layer 18. A number of conductive pillars 22 extend above the device layer 20 in order to connect the semiconductor die 12 to a carrier such as a printed circuit board (PCB), as discussed below. The surface of the device layer 20 opposite the insulating layer 18 provides a frontside of the semiconductor die 12, while the surface of the substrate 16 opposite the insulating layer 18 provides a backside of the semiconductor die 12.
One or more of the components 14 are then trimmed using a laser trimming process from the frontside of the semiconductor die 12 (step 102 and FIG. 3B). Specifically, a laser 24 is focused on one or more fuses (not shown) in one or more of the components 14 that are either openly exposed or exposed through a transparent or semi-transparent material in order to cut or destroy the fuses and thus adjust the resistance, capacitance, and/or inductance of the one or more components 14. The semiconductor die 12 is then flipped and attached to a carrier 26 such as a PCB (step 104 and FIG. 3C).
Performing the trimming process as described above suffers from several disadvantages. When the semiconductor die 12 is flipped and attached to the carrier 26, the operating parameters of the circuit formed by the components 14 may significantly change due to parasitics between the semiconductor die 12 and the carrier 26, mechanical stress, and other variables. However, since the components 14 are only available for trimming via the frontside of the semiconductor die 12 (i.e., since the components 14 are only accessible by the laser 24 from the frontside of the semiconductor die 12), the resistance, capacitance, and/or inductance of the components 14 can no longer be adjusted after the device is mounted on the carrier 26. Accordingly, these changes in the operating parameters of the circuit formed by the components cannot be compensated for.
In addition to the above, trimming the components 14 from the frontside of the semiconductor die 12 may require significant energy when the components are located at a significant depth within the device layer 20, since the energy required to cut or destroy a fuse is proportional to a depth of the fuse in the material in which it is surrounded and the thickness of the metal used to form the fuse. Generally, the closer the metal layer to the backside of the semiconductor die 12, the more energy required to trim the metal layer. Cutting or destroying a fuse generally results in damage to the area surrounding the fuse. An increase in the amount of energy required to cut or destroy a fuse results in a proportional increase in the severity of the damaged area and the size of the damaged area. Accordingly, trimming the components 14 from the frontside of the semiconductor die 12 may result in a significant amount of damage to the areas surrounding the fuses, and thus may decrease the performance of the semiconductor die 12. Due to the relatively large amount of energy used in the conventional trimming process, the fuses in the components 14 of the semiconductor die 12 are often spaced to ensure that damage from the trimming process does not affect the operating of the device. This often results in a large area required for the fuses, thereby increasing the size of the components 14 and the semiconductor die 12.
In light of the above, there is a need for improved methods for trimming components formed on a semiconductor die in order to adjust one or more operating parameters thereof.